Despite continued improvements in diagnosis, surgical techniques, and chemotherapy, breast cancer patients are still being overcome by cancer metastasis. Breast cancer metastasizes to brain, lung, bone, liver and regional lymph nodes. Early detection and advancements in research have increased survival and enhanced quality of life. However, there Is still a need for improvement. Tumor cell proliferation, invasion, and metastasis are known to be mediated, at least in part, through degradation of basement membrane by neutral metalloproteinases (MMP) produced by tumor and stroma cells. Evidence suggests that MMP-9 plays a significant role in breast tumor cell invasion and metastasis. We have shown that DNAzyme generated against MMP-9 mRNA was able to reduce the expression of the enzyme in vitro and its intratumoral injection reduced the size of mammary tumor, generated in a MMTV- PyMT transgenic mouse model, by 50%. DNAzymes are catalytic DNA molecules that specifically bind and cleave mRNA of the targeted protein, resulting in decreased protein expression. Given their potential for systemic administration and targeting, anti-MMP-9 DNAzyme (AM9D) could prove useful as a therapy against breast carcinoma invasion. We hypothesize the down regulation of MMP-9, by AM9D, will lead to the inhibition of tumor growth, decrease in lung metastasis, block experimental metastasis and increase survival in breast carcinoma animal model. Towards the achievement of this goal we propose to (1) determine the minimum effective dose of AM9D needed to significantly decrease tumor load in the PyMT MTEC transplant mouse model without causing significant local toxicity. Toxicity will be determined by histopathological analysis of tissue slices. (2) assess the affect of AM9D on development of secondary tumor. Luciferase expressing PyMT MTECs will be transplanted into female mice mammary glands of female mice and tumors will be treated with an optimum concentration of AM9D, control DNAzyme or PBS for 4 weeks. Tumors will then be removed and animal will be maintained for an additional 8 weeks to develop lung secondary tumors. In addition, experimental metastasis will be performed by injecting PyMT MTEC with or without AM9D or control DNazyme into tail vein of FVB/Nj mice. Formation and development of lung metastasis will then be followed by in vivo Xenogen bioimager system. (3) The effect of DNAzyme treatment on the survival rate of animals bearing breast carcinomas will be assessed. Thus, in this proposal we are taking an innovative approach to the treatment of breast carcinomas by studying the effect of the AM9D therapy on tumor growth and metastasis, the major mechanism of morbidity and mortality.